Rotor assemblies for an electric device, including but not limited to an induction electric motor, typically include a laminated stack of electric steel sheets that support a plurality of conductor bars disposed within longitudinal grooves defined by the laminated stack of electric steel sheets. The conductor bars extend outward beyond axial end surfaces of the laminated stack of electric steel sheets. The rotor assembly includes a first end ring and a second end ring disposed at the opposite axial end surfaces of the laminated stack of electric steel sheets. The first end ring and the second end ring electrically connect the ends of the conductor bars at the respective axial end surfaces of the laminated stack of electric steel sheets. The first end ring and the second end ring may be cast in place from aluminum over the ends of pre-formed conductor bars that re positioned in the longitudinal grooves of the laminated stack.
When the first end ring and the second end ring are cast in place over pre-formed conductor bars, interfacial bonding between the cast end rings and the pre-formed conductor bars, i.e., the bond between the cast end rings and the pre-formed conductor bars, is critical to the integrity of the rotor assembly. For example, if aluminum oxides are present on the pre-formed conductor bars when the end rings are cast in place, the aluminum oxides may prevent and/or reduce the quality of the bond between the cast in place end rings and the pre-formed conductor bars.